1. Field of the Invention
The present invention relates to a zoom lens apparatus for use in a liquid crystal projector, a television camera for industrial use or the like, more particularly, to a lens barrel for use in a zoom lens apparatus.
2. Description of the Related Art
A typical zoom lens apparatus employed in a liquid crystal projector, a television camera for industrial use or the like is constructed so that a cam barrel is freely fitted into a fixed barrel. The fixed barrel holds a lens system such as a zooming lens. The cam barrel is made to rotate around an optical axis to move the lens system in a direction parallel to the optical axis (hereinafter xe2x80x9cthe optical axis directionxe2x80x9d). That is, guide holes consisting of an elongated hole extending parallel to the optical axis are formed in the fixed barrel and support pins are provided on the outer periphery of a lens mount that holds the lens system while projecting into the guide holes. Further, elongated holes constituting cams are provided in the cam barrel along a direction tilted appropriately relative to the optical axis direction. Still further, the support pins are freely inserted into the cams. This construction allows the lens system to move in the optical axis direction guided by the guide holes while being limited in its moving distance by the oblique orientation of the cams.
In recent years, there has been a strong demand for an optical device such as a liquid crystal projector provided with highly sophisticated optical performances. That is, the liquid crystal projector is required to project images clearly onto a screen even when the amount of light emitted from a light source incorporated therein is small. For this reason, in such a liquid crystal projector, it is required that a lens having a small F value is employed in the optical system. In addition, the optical system is required to increase its magnification ratio so as to be able to project an image of copy filled with small characters in clear detail. Such strong demand for highly sophisticated optical performances to be realized in the optical system may cause the following problems in the conventional lens barrel for use in a zoom lens apparatus.
In the conventional lens barrel, to ensure advantages, such as simplicity of assembling operation, ease of operation for adjusting each part, continuing resistance to thermal deformation and the like, an appropriate gap as an allowance between parts is intentionally provided (when needed) or the number of parts to be employed is reduced by reducing the number of connecting parts provided between the parts. However, even such a microscopic event that a negligible gap causes the positional distortion of the lens in the optical axis direction may adversely affect the optical performance, thereby possibly disturbing realization of highly sophisticated optical performance to be achieved in an optical device.
In consideration of the above-described problems, the present invention has been conceived. That is, an aspect of the present invention is to provide a lens barrel for use in a zoom lens apparatus to securely be able to address the needs for developing optical devices with highly sophisticated optical performance.
A lens barrel for use in a zoom lens apparatus according to the present invention comprises: a fixed barrel holding a zoom lens system, and a cam barrel freely fitted to the fixed barrel and made to rotate around an optical axis direction as an axis with respect to the fixed barrel to move the zoom lens system in the optical axis direction, in which the fixed barrel is further constructed such that an appropriate number of radial supporting projection constituting a part of an outer periphery of the fixed barrel and projecting an appropriate length in both a circumferential direction of the fixed barrel and the optical axis direction are provided on portions of the fixed barrel, the portions being located in correspondence with ends of the cam barrel while facing the associated ends thereof, and the cam barrel is supported by the supporting projections.
As the cam barrel is supported by the supporting projections, the area where the cam barrel and the fixed barrel are in contact with each other can be made small to the utmost. Therefore, the cam barrel can be made to rotate smoothly with respect to the fixed barrel.
In general, it is desirable that a zoom lens apparatus is assembled in small size and is light in weight, and further can be provided at a low price. For this reason, it is required that the fixed barrel be formed by injection molding or the like using a synthetic resin and the cam barrel be formed by processing and molding a metal such as aluminum. Note that in the case where both the fixed barrel and the cam barrel are made of a metal, manufacturing cost of a zoom lens apparatus is forced to increase, and in the case where they both are made of a synthetic resin, there possibly arises a problem that accuracy with which a zoom lens system operates in response to the rotational movement of the cam barrel varies, whereby the zoom lens apparatus cannot maintain its desired accuracy.
In the case where the fixed barrel is formed by molding a synthetic resin and the cam barrel is formed by molding a metal, as those materials have their respective coefficients of thermal expansion different from each other, there possibly arises a problem that when the fixed barrel is thermally deformed, the cam barrel cannot be rotated smoothly. In addition, in the case where the area where the fixed barrel and the cam barrel are in contact with each other is large, possibility of causing the above-described problem increases. Specifically, in such an optical device as a liquid crystal projector, as a light source generating heat is disposed next to the zoom lens apparatus, the lens barrel is easily affected by the heat. In order to address such a serious problem, as shown in the lens barrel of the present invention, the fixed barrel is formed to have supporting projections thereon such that the supporting projections are made in contact with the inner periphery of the cam barrel for guiding the cam barrel into rotational movement, thereby enabling the cam barrel to rotate smoothly to the utmost even in a state of the fixed barrel being thermally deformed.
Furthermore, the lens barrel for use in a zoom apparatus in accordance with the present invention is constructed such that the supporting projections are provided on respective ends of the fixed barrel and spaced at equal intervals, and further, the supporting projections on the respective ends of the fixed barrel are provided facing each other.
In the case where the fixed barrel is processed by using a synthetic resin, as the supporting projections on front and rear ends of the fixed barrel are provided facing each other, operation for designing a molding die assembly becomes easier.
Additionally, the lens barrel for use in a zoom lens apparatus in accordance with the present invention is constructed such that the supporting projections are provided on respective ends of the fixed barrel and spaced at equal intervals, and further, the supporting projections are alternately disposed at front and rear ends of the fixed barrel in the circumferential direction thereof.
In the event the fixed barrel is thermally deformed, the construction that the supporting projections are alternately disposed at front and rear ends of the fixed barrel in the circumferential direction thereof makes it possible to permit the deformation to equally act on the cam barrel, thereby enabling the cam barrel to maintain its smooth rotation to the utmost.
Additionally, a lens barrel for use in a zoom lens apparatus in accordance with another aspect of the present invention comprises: a fixed barrel holding a zoom lens system and at the same time, a focus lens system in a front end thereof; a cam barrel freely fitted to the fixed barrel and made to rotate around an optical axis direction as an axis with respect to the fixed barrel to move the zoom lens system in the optical axis direction; and an input member fixed to the cam barrel to rotate the cam barrel, in which the cam barrel comprises a control section formed on an outer periphery of the cam barrel for restricting movement of the input member in the optical axis direction to thereby limit the degree of longitudinal engagement of the input member with the cam barrel.
In order to enhance compactness of a zoom lens apparatus, the zoom lens apparatus is often designed so that a part of one component and a part of another component, both components being attached to a projection lens barrel, are made to overlap each other in the optical axis direction. In the case where a focus lens system is held at the front end of a fixed barrel, a part of a drive member of the focus lens system and a part of an input member of a zoom lens system are made to overlap each other in the optical axis direction. Those members are formed annular, and further, the inner annular member is to be attached to a lens barrel such as a cam barrel at the portion thereof where those members are overlapped with each other. Therefore, once the outer annular member is attached to the lens barrel in advance, the phenomenon that the inner annular member cannot be attached thereto may occur. In such a case, when the assembling of the outer annular member is finished, the outer annular member is being attached to locate outside the surface area that the inner annular member will occupy when attached to the associated position. Thus, after the inner annular member is attached to the associated position, the outer annular member is made to move to the position to be attached and then attached thereto while being fixed thereto.
That is, in the case where the input member is the outer annular member and a drive member holding the focus lens system is the inner annular member, the input member is made to fit into the cam barrel while being located outside the surface area that the drive member will occupy when attached to the associated position. In this case, the input member will later on be moved back sliding on the cam barrel to the position to be attached. The moving range needed for the input member to move to the position located outside the surface area that the drive member will occupy when attached to the associated position is limited by the control section to prevent the input member from moving beyond the moving range, thereby enabling the operation for assembling the drive member and the input member to be simplified.
Furthermore, the lens barrel for use in a zoom lens apparatus in accordance with the present invention is constructed such that a moving speed of a processing tool is made different when the outer periphery of the cam barrel is processed, in such a manner that the moving speed thereof is made low to process one area of the outer periphery of the cam barrel ranging from a front end to an appropriate position of the cam barrel with high accuracy and the moving speed is made high to process the other area of the outer periphery of the cam barrel, whereby surface areas having different processing accuracies are formed on the outer periphery of the cam barrel and a boundary between the surface areas having different processing accuracies constitutes the control section.
In the case where the cam barrel is made of a metal and the outer periphery thereof is processed by a lathe, the outer periphery thereof is processed with high accuracy to have fine roughness thereon by making the moving speed of the cutting blade low, thereby forming a sliding surface thereon for the input member to be able to smoothly move on the sliding surface. On the other hand, the outer periphery thereof is also processed to be a roughened surface by making the moving speed of the cutting blade high. Therefore, a boundary between the sliding and roughened surfaces can be defined as the control section. That is, the input member can smoothly move on the outer periphery of the cam barrel since the outer periphery thereof at a front section thereof is processed to be a sliding surface. In addition, as the outer periphery thereof other than the sliding surface is formed to be a roughened surface, the input member cannot move on the roughened surface, thereby permitting the input member to move only within a range of surface area, the range being determined to include a surface area to a minimum that the drive member needs when attached to the associated position. Moreover, after the drive member is attached to the associated position, the input member can easily be moved to the position to be attached.
Additionally, the lens barrel for use in a zoom lens apparatus in accordance with the present invention is constructed such that an outer diameter of the cam barrel is made different at the boundary between the surface areas having different processing accuracies to prevent the input member from moving beyond a high accuracy area out of the surface areas, the high accuracy area being processed with high accuracy.
As the input member is fitted into the cam barrel having a gap with respect thereto, even in the case where the other surface area other than a surface area of the cam barrel is processed with high accuracy, i.e., a sliding surface is formed having a roughened surface, when an external force happens to be applied to the input member, the phenomenon that the input member falls into the state thereof being squeezed into the cam barrel at the position of the roughened surface thereof could occur. When the input member under such state is forcibly going to be moved to the position to be attached, the phenomenon that the input member is locked staying on the roughened surface by the frictional force generated therebetween. Therefore, non-movement may occur.
Accordingly, the construction that the outer diameter of the other surface area other than the sliding surface is made larger than that of the sliding surface prevents the input member from moving beyond the surface-area having the sliding surface.
Moreover, the lens barrel for use in a zoom lens apparatus in accordance with the present invention is constructed such that the fixed barrel is formed by molding using a synthetic resin and the cam barrel is formed by molding using a metal.
The construction that the fixed barrel is molded from a resin and the cam barrel is molded from a metal enables the zoom lens apparatus to drive a projector lens with high accuracy, i.e., in a manner that is free from damage to its optical performances. Further, increase in the manufacturing cost of the zoom lens apparatus is suppressed.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.